iii
The research effort is oriented towards the modeling of metal powder sintering to
accurately predict the densification and distortion of a sintered part, which is mainly due
to the differential shrinkage of a green compact. This research focuses on the study of the
simulation of the sintering process that is dominated by grain boundary diffusion, which
is recognized as one of the dominating sintering mechanisms. Specifically, a
viscoelasticity model that accounts for the microstructural grain growth has been
developed to simulate the thermal induced creep deformation in sintering. Sintering stress
is treated as an equivalent hydrostatic pressure that links the microscale evolution to the
macroscale deformation. To support that linkage, a grain boundary counting procedure
has been modified to quantify the grain size distribution. The material resistance of
viscous flow is included in the model as a thermally activated process using an
Arrhenius-type temperature relation to represent the apparent viscosity.
The finite element method is used to implement the simulation. Results of the
compaction simulation such as shape change, residual stress and density distribution data
are transferred into the sintering simulation as initial conditions. Since no extra heat
source is generated during sintering, the thermal analysis is independent of the creep
analysis so that an uncoupled heat transfer analysis yields time-dependent temperature
fields that are used to drive the sintering simulation. The simulation is performed in
ABAQUS, and an in-house FEM code (SinSolver) is used as a supporting tool and
verification.
iv
Stainless steel 316L is chosen in this research due to its wide range of industrial
applications and representative sintering mechanisms. Comparison and analysis on the
simulation versus the dilatometry experiments of shrinkage are consistently close and
improve the understanding of when and how the sintering mechanisms act in a sintering
cycle.